"I hope everyone has buckled their seatbelts because the outer Solar System just got a lot weirder, " Michele Bannister, an astronomer at Queens University, tweeted on Monday.

Orbiting to the beat of a different drum

The object is about 160,000 times fainter than Neptune, suggesting that it could be less than 120 miles in diameter. That makes the icy celestial body a minor planet, which means it's smaller than a planet but not quite a comet.

Here's where things get weird.

Niku orbits the solar system at a bizarre angle: a plane tilted 110 degrees to the flat plane of the solar system. This flat plane of the solar system — a disk in which planets move around the sun — is a defining quality of a planetary system.

But Niku, already moving above the plane, travels a little further upward every day.

And unlike the other law-abiding objects in the solar system, Niku travels against the flow of the bulk of the solar system, taking a wild backwards swing around the sun.

Objects that don't move within the plane of the solar system or spin in the opposite direction must have been shoved off course by something else or tugged by the gravity of another object.

"It suggests that there's more going on in the outer solar system than we're fully aware of," Matthew Holman at the Harvard-Smithsonian Center for Astrophysics, part of the team that discovered Niku, told New Scientist, where we first saw the story.

Hanging with the wrong crowd

Scientists noticed that rebel Niku seems to be hanging around a gang of other strangely aligned objects. At first glance, the scientists thought this might suggest that Planet Nine, a hypothetical planet that would be about 10 times as massive as Earth, might be pulling on the objects.

But it turns out that the rebellious object would be out of Planet Nine's reach, too free-living to succumb to the undiscovered planet's gravitational attraction.

So exactly what's going on is still a mystery.

"As they say in the paper, what they have right now is a hint," Konstantin Batygin, one of the researchers who suggested the existence of Planet Nine, told New Scientist. "If this hint develops into a complete story that would be fantastic."